The important relationship of diet and nutrition in the development of cancer has become well known through various research efforts. Laboratory studies have shown cancer inhibitory functions for various natural and synthetic nutrients in various models, which have been corroborated by human epidemiologic studies of nutrient intake, tissue levels and cancer incidence. Vitamin A, beta-carotene and selenium have been strongly implicated for their cancer preventive potential, with evidence for the former two substances warranting clincical trials of their efficacy. In addition, the roles of other nutrients in cancer cause and prevention (e.g., dietary fats and fiber) require further investigation. The objectives of the project are: 1) to determine if beta-carotene supplementation is effective in preventing lung cancer in smokers; 2) to better assess the role of selenium, vitamins A, E, and C, and fats in breast cancer development; 3) to investigate the role of various nutrients (in prenatal maternal blood) for the development of cancer in children, and 4) to evaluate the roles of various levels of nutrient intake to subsequent cancer. The project includes four studies all of which take place in Finland. The first, a beta-carotene, lung cancer intervention trial, is a five-year, double-blind, placebo-controlled, randomized trial of daily beta-carotene supplementation (15 mg. orally) among cigarette smokers. Any reduction of lung cancer incidence in the beta-carotene group will be measured. The second is a breast cancer case control study of selenium, vitamins A, E, C, fats and other nutrients (both serum levels and dietary history), using both benign breast disease and neighborhood controls. The importance of these nutrients in breast cancer development will be assessed. The dietary survey study will use previously collected dietary history information for a subgroup having developed cancer out of our original population cohort. Associations between various dietary components and different cancers will be assessed. The fourth study is a case-control investigation of prenatal maternal nutritional status (i.e., nutrient blood levels) and subsequent early childhood cancer incidence in those offspring.